Flammability measurements of difluoromethane

Difluoromethane (CH2F2, or R-32) is a candidate to replace ozone-depleting chlorofluorocarbon refrigerants. Because CH2F2 is flammable, it is necessar y to assess the hazard posed by a leak in a refrigeration machine. The curr ently accepted method for determining flammability, ASTM E 681 has difficul ty discerning the flammability boundary for weak fuels such as CH2F2. This article describes an alternative approach to identify the limits of flammab ility, using a twin, premixed counterflow flame. By using the extinction of an already established flame, the point dividing flammable from nonflammab le becomes unambiguous. The limiting extinction mixture changes with stretc h rate, so it is convenient to report the flammability limit as the value e xtrapolated to a zero stretch condition. In the burner, contoured nozzles w ith outlet diameters of 12 mm are aligned counter to each other and spaced 12 mm apart. The lean flammability limit of CH2F2 in dry air at room temper ature was previously reported by the authors to be a mole fraction of 0.14, using the twin counterflow flame method. In the current study, relative hu midity was not found to affect the lean limit. Increasing the temperature o f the premixed fuel and air to 100 degreesC is shown to extend the flammabi lity limit in the lean direction to 0.13. The rich limit of CH2F2 found usi ng the counterflow method is around 0.27. The uncertainties of the measurem ents are presented and the results compared to data in the literature.